Black-pigmented Bacteroides species have been implicated in the pathogenesis of periodontal and periapical diseases. Surface components may contribute to the pathogenicity of oral Bacteroides, as has been demonstrated for Bacteroides fragilis and other non-oral bacteria. Specifically, capsular polysaccharides from many bacterial species have been implicated in the inhibition of the alternative complement pathway and/or impaired phagocytosis and killing of bacteria by neutrophils. Therefore, the polysaccharide capsule may represent a major virulence factor in oral Bacteroides. The aim of this proposal is to examine the capsular polysaccharides from oral Bacteroides in order to elucidate their role in the pathogenicity of these organisms. Initial work will focus on B. gingivalis and B. intermedius. The capsular polysaccharides from multiple strains will be visualized by electron microscopy with ruthenium red staining. Polysaccharides from selected strains will be extracted by the hot phenol-water technique, purified by column chromatography, and chemically and structurally characterized by various techniques including gas chromatography and gas chromatography/mass spectroscopy. Specific antisera will be raised to the polysaccharides to facilitate intraspecies and interspecies comparisons and to examine the possible role of the extracellular polysaccharides as serogroup antigens for subgroups of B. gingivalis and B. intermedius. The structure of the determinants will be examined using serological inhibition assays with component saccharides and modified capsular polysaccharides. Purified extracellular polysaccharide and bacteria with varying degrees of encapsulation will be employed in both in vitro and in vivo assays to evaluate the role of the polysaccharide in the expression of virulence. Serum sensitivity, complement activation, requirements for opsonization, and neutrophil bactericidal activity will be examined. The protective potential of immunization with extracellular polysaccharide to prevent bacteremia, secondary abscess formation, and modification of primary abscess formation will be evaluated in the mouse model. Also, the human antibody response directed toward the capsular antigen will be tested at clinically defined stages during the treatment of periodontal disease. These studies should contribute to elucidating the potential role of Bacteroides exopolysaccharide in the etiology of oral anaerobic infections and could provide a rationale for the development of vaccines for clinical management of these infections.